An ideal cancer therapeutic agent would specifically target malignant cells to kill these cells while avoiding normal tissues. Oncolytic viruses are viruses developed to selectively kill tumor cells by infecting, replicating, and ultimately killing these cells. These agents have the appeal of being self-amplifying drugs, because each infected tumor cell produces 10,000 more viruses to amplify the number of killed tumor cells. Oncolytic viruses have shown promise in preclinical and clinical trials where they have proved most useful when applied by direct intratumoral injection. While this may be useful for debulking tumors, this approach cannot address distant metastases. Adenoviruses have been engineered to achieve cancer specificity by taking advantage of specific traits of certain cancer cell types or by taking advantage of molecular changes intrinsic to oncogenesis. While these viruses have higher cancer specificity, loss of 90% of the intravenously injected dose to liver reduces the amount of virus available to kill tumor metastases. This loss also produces dose-limiting and sometimes lethal liver damage. In addition to these pharmacologic problems, another significant hurdle to clinical translation is the presence or high levels of neutralizing antibodies against Ad5 in patients. These antibodies deplete most of an injected dose markedly reducing efficacy. Given these problems, this project will apply clinically-relevant interventions to attempt to improve both the pharmacology and immunogenicity of adenoviral oncolytics for systemic cancer therapy. This project will detarget oncolytic viruses from the liver and shield them from the immune system by genetic and chemical engineering. The Molecular Medicine Program at Mayo Clinic has previously translated other oncolytic viruses into the clinic for cancer applications. If this project is successful, it will therefore lay the groundwork for translating these adenovirus oncolytics for the treatment of cancer patients at Mayo Clinic and other sites.